The cornea is the transparent, shiny membrane that makes up the front of the eyeball. There are three layers in the cornea, all of which are highly specialized skin cells. The outermost layer is the epithelium, which is a very thin layer of cells. Below the epithelium is the stroma, which is the main supportive tissue of the cornea, and the deepest layer is Descemet's membrane where endothelial cells grow. Because all of these layers of the cornea are clear, it is not possible to see them without special stains that color specific cells and highlight them when the tissue is examined under a microscope.
What is a corneal ulcer?
Erosion of a few layers of the epithelium is called a corneal erosion or corneal abrasion. A corneal ulcer is deeper erosion through the entire epithelium and into the stroma. With a corneal ulcer, fluid is absorbed from the tears into the stroma, giving a cloudy appearance to the eye. If the erosion goes through the epithelium and stroma to the deepest level of Descemet's membrane, a descemetocele is formed. A descemetocele is a very serious condition. If Descemet's membrane ruptures, the liquid inside the eyeball leaks out, the eye collapses and irreparable damage occurs.
There are several causes for corneal ulcers, and they occur most commonly due to trauma to the eye. Superficial corneal abrasions can occur from physical or chemical trauma such as:
- Rough play with other dogs/animals
- Running through heavy vegetation or woods
- Irritating substances such as shampoo or dust/debris
- Infection or bacteria (less common)
- A cat scratch or a sharp object (which can cause more serious damage)
Corneal ulcers are also common in certain breeds with underlying diseases such as:
- Dry eye, where decreased production of tears leads to drying of the corneal surface
- Brachycephalic (flat-faced) breeds with prominent eyes (such as Boston Terriers, Pugs, Shih Tzu’s, Boxers, and Bulldogs)
A corneal ulcer is very painful. Most animals rub the affected eye with a paw or on the carpet in an attempt to relieve this intense pain. To protect the eye, they keep the lids tightly closed. Occasionally, a discharge will collect in the corner of the eye or run down the face.
Fluorescein dye test: A drop of this stain is placed on the cornea. The dye will turn green and adhere to areas of ulceration. A fluorescein stain test is the most common eye test performed to rule out a corneal ulcer. Based on the results medications are prescribed.
Corneal abrasions generally heal within three to five days. Medication is used to prevent bacterial infections (ophthalmic antibiotic drops or ointment), and to relieve spasm and pain (typically ophthalmic atropine drops or ointment). It is very important that corticosteroids (steroids) are not used in the eye as they delay the healing process.
An eye culture is required in some chronic cases when the ulcer is not healing to check for what antibiotics the eye will be most sensitive to.
If a corneal ulcer or a descemetocele is present, steps must be taken to protect the eye and to promote healing. Since animals do not wear eye patches well, surgery may be required to protect the injury and allow for normal healing. In certain cases, it may be necessary to perform surgery to remove dead or poorly healing layers of corneal tissue (grid keratectomy), third eyelid flap or to perform a corneal graft.
A cone collar is required to prevent your pet from scratching their eyes during the course of treatment.